1. Field of the Invention
The present invention relates to a protein, which regulates rice-derived environmental stress tolerance, a gene encoding the same, and a method for utilizing the same.
2. Prior Art
Plants possess tolerance mechanisms to cope with various types of environmental stresses in nature such as dehydration, high temperature, freezing, or salt stress. In the production of plants having such environmental stress tolerance, techniques have been heretofore used for genetically selecting and mating strains which are dehydration, salt, or low temperature tolerant. However, these techniques require long periods of time to select, and also have low success rates.
On the other hand, as the stress tolerance mechanism is elucidated at a molecular level, stress tolerant plants have been produced using biotechnological techniques. For example, it has been shown that stress proteins such as LEA proteins, water channel proteins, or synthetases for compatible solutes are induced in cells when they are exposed to stress, thereby protecting the cells from such stress. Thus, research has been attempted in which genes such as LEA proteins of barley or detoxification enzymes of tobacco, or genes of synthetases for osmoregulatory substances (e.g., sugar, proline, or glycinebetaine) are introduced into host plants. Research using genes encoding w-3 fatty acid desaturase of Arabidopsis thaliana, the D9-desaturase of blue-green algae, or the like, which are modification enzymes of the cellular membrane lipid, has also been attempted. In the above researches, a gene was bound to the 35S promoter of cauliflower mosaic virus and introduced into a plant. The level of stress tolerance of the recombinant plant was, however, low and unstable. Thus, none of these was put to practical use.
On the other hand, stress tolerance mechanism is found to be intricately associated with several genes (Plant Physiol., 115: 327-334 (1997)). Accordingly, research in which a gene encoding a transcription factor which simultaneously activates the expression of the genes is introduced into a plant, thereby enhancing the plant's stress tolerance, has been attempted (The Plant Cell, 10: 1-17 (1998)). However, when several genes are simultaneously activated, the energy of the host plant becomes directed towards the generation of the gene product or intracellular metabolism resulting from the gene product. Accordingly, the growth of the plant itself deteriorates or becomes retarded.
In contrast, the present inventors had isolated the genes DREB1A, DREB1B, DREB1C, DREB2A, and DREB2B encoding the transcription factors which bind to a stress responsive element and specifically activate the transcription of genes located downstream of the element from Arabidopsis thaliana (Japanese Patent Application No. 10-22847, Laying-Open (kokai) No. 2000-60558). They reported that introduction and overexpression of the genes in a plant enabled impartment of stress tolerance without causing retardation of a plant (Japanese Patent Application No. 10-292348, Laying-Open (kokai) No. 2000-116260).
Arabidopsis thaliana is classified as a dicotyledonous plant while major crops such as rice, maize, and wheat are classified as monocotyledonous plants. Dicotyledonous plants are relatively different from monocotyledonous plants from the viewpoint of plants evolution. It has been shown that the DREB1A gene of Arabidopsis thaliana functions well in monocotyledonous plants, but not as well in dicotyledonous plants. Thus, if a DREB-homologous gene derived from the monocotyledonous plant can be isolated, environmental stress tolerance can be more efficiently transmitted to monocotyledonous plants thereby.